We actually were lucky enough a few weeks back, to book 13 free nights in California in Aug, both for ourselves, and the other family travelling with us. (What are friends for??)
Now, it seems those locations are much more difficult to find the lower rates for...it seems once they get burned, they tighten up the available rates very quickly.
They are also all franchises, and one hotel owner was so upset when he received notification of our two free night bookings, he called right away, which happenned to be in the middle of the night for us, with the time difference! Not amusing! I am sure he will not be amused either, when we show up, and he has to choice but to award the free night! On the phone call, he was offering to match the lower price we found...so it remains to be seen how he deals with it.
I inquired through the Triprewards Guarantee office, and asked the what if scenario, and they told me if he says you MUST pay, then go ahead and pay, and the submit through head office. They will reimburse, and also charge him a fee.

Canada1